FLOW OF ABYSSAL WATER INTO THE SAMOA PASSAGE

On the TEW Expedition a hydrographic section was made in June 1987 across the Samoa Passage; in addition, south of the Passage, a section was made through the Penrhyn and Samoa Basins and the Tonga Trench. In this paper the flow of the deep water with North Atlantic Deep Water and Antarctic characteristics below 3500 m is discussed. Temperature-salinity-oxygen relationships show a similarity of properties between the Tonga Trench and western boundary of the Samoa Basin. The salinity and silicate date show distinct signatures of North Atlantic Deep Water and Antarctic Bottom Water flowing into the Samoa Passage. Salinity and silicate data in the Samoa Basin and Passage are similar to those measured on the STYX Expedition (1968). Oxygen data show that the water along the Samoa Basin's western boundary is oxygen-rich relative to water in the eastern Basin, but with no oxygen maximum in deep water, as was observed on STYX. Geostrophic flow, based on a reference surface determined from T-S, O2 curves, shows strong northward components (> 10 cm s-1) in the Samoa Passage. On the west side of the Passage the flow was southward (< 1 cm s-1) below 4600 m. This flow reversal was associated with a reversal of the sign of the horizontal potential temperature gradient and also with lower values of oxygen, salinity and silicate next to the boundary. The northward transport of Lower Circumpolar Water between the Manihiki Plateau and the Tonga Trench was 12.3 +/- 3.6 x 10(6) m3 s-1; the flow into the Samoa Passage was 6.0 +/- 1.1 x 10(6) m3 s-1. Assuming that only flow above 4800 m can exit the northern Samoa Basin because of topographic restrictions, the total northward transport into the north Tokelau Basin was 9.6 +/- 1.8 x 10(6) m3 s-1.